The objective of our research is to examine the role of ligase, DNA polymerase and exonuclease in the replication and recombination of T4 bacteriophage DNA, and late messenger RNA synthesis. We shall use conditional lethal mutants in genes which regulate these enzymes. T4 genes 46 and 47 seem to regulate an in vivo exonuclease which produces internal (and/or external) single stranded regions on nicked T4 DNA. These genes seem to be necessary for the first step of biparental molecular recombination and also for producing and maintaining the structure of phage precursor DNA. Relations between recombination and the structure of the T4 precursor DNA are being examined. The biochemistry of DNA and RNA oncogenic viruses has been shown to involve various enzymes related to DNA metabolism during infection, integration and the induction of cancer. This process includes infection of the host cell and integration of the host chromosome. Current laboratory research on these viruses is focused on the metabolism of DNA, using information that has resulted from studies of bacterial viruses.